Just looking at your posted photos on my PC as it's a much bigger screen than my phone.

That is some pretty tight quarters there to start digging into for sure.

The engine I checked back then was the one in the shed that was over heated, it was not warmed up either as it wasn't even in a vehicle, it was in the back of my work truck on blocks.I have the 720 to drive so I am not all that excited about digging into the 521 engine again any time soon, I am undecided on if I should look at the diaphragm, or just switch out injection pumps, the only spare I would take off anything had WVO put through it, it ran alright, but it didn't have the power my other SD25 had, it had the power of an SD22, so I am not all that thrilled with the idea of switching out a suspect used pump for another suspect used pump just to see if anything changes.I would have to tear apart my rebuilt SD22 engine to get everything I need to change over to a VE type injection pump taking yet another engine apart that is complete, I don't like taking apart complete engines, and the VE injection pumps I have are SD22 pumps.Are the inline injection pumps on the SD25 engines the same injection pumps that are on the SD22 engines just turned up?

_________________I know the voices are not real, but they have some really good ideas.

Wow. Ten pages in this thread. I admit, I limited myself to 30 minutes, so I skimmed.

Wayne has been very helpful reminding me when the forum server has gone to sleep, and he asked me to weigh in on this thread.

Fuel delivery issues. Gawd, how many times have I been down this path.

1) Pre-filter. It's been mentioned upthread but bears repeating: A PAPER PRE-FILTER CANNOT BE USED ON A DIESEL. They all lack enough surface area to flow enough fuel with diesel's viscosity. You may as well read my Tale of Woe on my own experience accidentally substituting a gas paper fuel filter for the OEM Nissan wire mesh filter.

3) Fuel quality. The pics of your fuel in clear containers makes the fuel look awful. If anything more than a tablespoon (liquid) or one-half teaspoon (solids) settles out, it should be separated and filtered (cheesecloth-type method) before reusing, or sent to hazmat (or used for bonfire).

5) Tank pickup restriction. Read gromit's tale. This kind of thing is more common than you think -- I've fought it at least four times over my careers.

6) Diagnosing fuel delivery problems. Quoting myself:"For fuel delivery problems, I use the same method most every time. I teed into the pressure line off the fuel pump, got out my old Sears vacuum/pressure gauge (it was old then; it's positively ancient today) and duct-taped it to the windscreen, connected it to the tee. Drove the truck. This time, I could see the fuel pressure falling off long before the truck began losing power. OK, fuel delivery problem confirmed."

Use the vacuum/pressure gauge, a tee, and some clear fuel line. Paste the gauge to the windscreen, and if you can make enough gap at the hood, also bring the clear fuel line up so a loop of it can be seen through the windscreen. Tee at the firewall or the fuel pump, not any further back. You need to know what's happening at the engine.

The vacuum/pressure gauge will tell all.

First, tee between the firewall hard line (from the rear/tank) to your prefilter. Run until you have a symptom/missing/loss of power. What does the gauge say? More than 1" vacuum? The restriction is somewhere between the firewall and the ass end. I've had crushed lines, rusted lines, lines filled with crap in the fuel, water (harder to pump that fuel), plugged vent line, rusted pickup tubes and probably others I'm forgetting.

No big vacuum on that test, but still loss of power? Move the gauge's test tee to the pressure side of the fuel lift pump. Repeat test drive.

Fuel pressure started high but dropped down under load or after a while? You've narrowed the problem to between the firewall and the fuel pump. I've seen plugged filter(s), collapsing inlet lines, and failed check valves in the fuel pump. Also, one defective filter head, I can't recall the details now.

Fuel pressure was good and stayed good, but still loss of power? Move the test tee to the line feeding fuel to the IP, repeat test.

Fuel pressure OK idle + under load? Has to be the IP or engine hard parts: you do not have a fuel delivery problem (delivery to the IP, that is). That said, the Inline IP is about the most robust part on a SDxx engine, so I would not condemn it lightly. Other than the leather diaphragm, they're as close to indestructible as an IP can be in consumer automotive-land, IMO.

I own (and sometimes even drive) a 1999 MB E300 (OM606.962 turbodiesel) these days, and it's infamous for air leaks (and fuel leaks) on the low-pressure (vacuum) side of the fuel system. I kid you not, there are SIX molded hard plastic fuel lines on the feed side, each with two o-rings to fail, four more o-rings on the main filter head, an electric shut-off valve with one obvious and two well-hidden o-rings, and a raft of other rubber lines and connections all waiting to prevent you from starting if the car's nose isn't pointed downhill, or if you have less than 1/4 tank of fuel. And they'll leak fuel, too, trying to ruin the large underbelly covers.

Air intrusion into the E300's fuel system is a fact of life. Oh, yes, I'm familiar with air getting in the system. Two words: clear tubing. You can use the cheap aquarium-quality stuff for a short test, as long as you are careful not to route it near hot things and not to let it abrade. Hood off, or careful routing out the grille, and you can run down the highway with 15' of the stuff plumbed in. You can see the stream of little bubbles as the fuel passes in front of your eyes on the windshield.

Change the coolant! Do it now! Don't worry about the cause unless it continues to turn color quickly. If you're not blowing the radiator cap pressure limit while driving under load, and there's no oily sheen in the coolant reservoir, chances are good the HG is OK. But there's crap circulating in the coolant from somewhere, and it needs to be let out. Flush the system as best you can. If you have a working heater, disconnect the hoses to the heater core and use a garden hose to flush in both directions, lots of water. The heater core is the de-facto filter for the cooling system. If you've ever hand-flushed a heater core when it's outside the vehicle (ie holding it in your hands) and shook it and flushed, shake and flush, you know what I mean: more crap comes out than you can believe can fit in that core.

You don't have to remove the core to do a half-decent job of removing the loosest crap, but do try to flush it when you're changing out the coolant.

8pm is coming, and that's my bedtime folks (I get up at 0330 these days, for commute to work), so that's all for now. Get out the old vacuum/pressure gauge, buy a plastic tee or fab one out of brass fittings, buy a bunch of clear fuel line, and get testing. It's easier to find the problem than you think.

OK, I will buy a vacuum/pressure gauge and start again.I believe the fuel lines are good as I have sucked fuel out of the tank with a clear line and my mouth, it came out easy.I also blew thru the hard line from the pre-filter connection to the tank with my mouth till I herd bubbles one time only.I have put clear lines between the tank and pre-filter, and between the fuel filter and IP feed line, I seen no air bubbles.This 521 kingcab is sitting on a 720 diesel frame using the diesel tank.I changed out the fuel pump/lift pump with a new one without any positive results.

I have been using gas pre-filters and have been for years on the 720 diesel without issues, I will get a diesel pre-filter, I liked the gas filters because I could see when they got dirty.I never thought about the EGT probe being after the turbocharger, I really don't have a place before the turbocharger to put it except maybe in the adapter, but I don't think there is enough room to weld the bung in the adapter, I will have to think about changing its location after I figure out this power loss issue.

I have a few cord of wood to pick up tomorrow and Friday, will not likely be working on this till Saturday at the earliest.

_________________I know the voices are not real, but they have some really good ideas.

Your testing of the fuel lines (can suck fuel) and air bubbles checking are static tests in your yard. You need the test data when you're driving and experiencing the power loss.

You don't have reduced power immediately, and the fuel is flowing fine when you pull out onto the street first thing after startup. Power loss happens later, and that's when you need the gauge setup and clear line, to show you what's happening in the fuel delivery system when the power loss occurs.

The 2" gas fuel filters won't work. I know you've been using them for years, but take my word for it: sooner or later they always give you grief, when you use them with diesel. They just do not have the capacity (surface area) to adequately flow.

I'm glad you're using a diesel tank.

I read about you having changed the lift pump already, but for completeness (other people read these threads, tool) I had to list all the causes I could think of.

If you don't want to buy the pressure/vaccum test gauge, I can mail you one. I'm certain I have at least two and probably three. Because I no longer own any older rolling stock, I don't work on things where that gauge is handy any more, and I picked up a couple over the years at swap meets.

I moved around two and a half cord of wood today, didn't do anything with the truck except start it twice to move it out of the way.Tomorrow I have a few things to do in the morning, then I will see about buying a vacuum/pressure gauge.

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_________________I know the voices are not real, but they have some really good ideas.

I started it up after putting a vacuum/pressure gauge in the injection pump feed line that goes from the out on the fuel filter housing to the front of the injection pump, that also has a clear line on it, I then drove it maybe 3 miles total, I had power loss after a mile, so I turned around and went home, the fuel pressure was so erratic that the needle fell off the shaft it was mounted on, but it lasted long enough for me to see a loss of fuel pressure.

The first thing I did was remove the lower banjo fitting on the lift pump and check the screen, it was clear.Next I removed the "in" banjo fitting on the fuel filter housing and blew air thru it, I then removed the upper banjo fitting on the lift pump(fuel pump) and the hose and blew air thru that to make sure it was clear, it was clear.Next I removed the fuel return banjo fitting and looked it over, it is the new one I put on after I replaced all the filters and had no improvement.I then removed the fuel filter housing and replaced it with the new fuel filter housing and put the new fuel filter on the new housing, I then put all the banjo fittings on the fuel filter housing, I then ran two lines to the rear box and put them in a gas can of diesel fuel I bought to bypass the fuel tank, I now have bypassed all lines to the tank, cleared all banjo fittings and lines, and I checked every line, and have bypassed or changed every line since this issue started on that trip to Hood River OR, there is nothing left to change except the return line from the injectors and that line returns back the the fuel tank via that two fitting banjo fitting on the fuel filter housing. I then started it up and checked for leaks, found none and took it for a drive, I drove it likely 20 miles total, it drove pretty good for the first 10/12 miles, I then turned around and headed back home, on the first big uphill incline I had power loss, I pulled over when it was safe and popped the hood and looked at the clear IP feed line and there was a bubble of air in it, the engine smoothed out and I hit the freeway again and had power loss at the next extended slight hill but my exit was at the top of that hill so I just kept driving, by the time I got to the signal to make my left(slower driving) I had my power back, I drove home without issues after that.

So I have a completely different fuel system to feed the injection pump except for the one line coming from the injectors to the fuel return circuit and I still have the same issue, I did see fuel pressure loss in the feed line to the injection pump, and I seen an air bubble in that line after the first power loss, somehow air is getting into the fuel filter housing, I have tried 3 different pre-filters without any change.

Another thing I noticed was after I first started the engine and the fuel pressure built up in the feed line, when I shut the engine down it took quite a while for the fuel pressure to bleed down in the feed line, but it slowly bled down, and again I will say that the fuel pressure was very erratic, the needle was bouncing all over the place, and hard enough to shake the needle lose from its shaft, the needle is just laying lose in the gauge now.

I have replaced every line since having the issue the first time, replaced the lift pump/fuel pump, replaced the tank with a temporary one, replaced the fuel filter housing and fuel filter, replaced the return line banjo fitting with a new one I had that was on the new fuel filter housing(sat in my parts room for years), different fuel, 3 different fuel pre-filters and nothing has changed.The only things I have not done is replace the diaphragm, remove the turbocharger.Now since I seen an air bubble in the IP feed line and I seen fuel pressure loss in the same line before the gauge broke from the fuel pressure being so erratic, I am assuming that the air is not getting into the injection pump thru the housing on the injection pump side of the diaphragm since I have boost on both sides of the diaphragm, but the air bubble could have been a fluke, can air get into the area where the feed line goes into the injection pump any other way?Could it somehow get in from the cavity behind the diaphragm where the code liver oil is supposed to be?Being the fuel pressure appeared to be way over 15psi in the feed line and pump, could 10psi boost even get in the injection pump where the fuel is pressurized?

_________________I know the voices are not real, but they have some really good ideas.

Don't run the engine without the final filter in place. That's not a good diagnostic to try.

waynosworld wrote:

Being the fuel pressure appeared to be way over 15psi in the feed line and pump, could 10psi boost even get in the injection pump where the fuel is pressurized?

According to this schematic (BTW: thanks so much for providing this):

. . . you are pressurizing the IP vent line as well as the throttle housing (and therefore the pneumatic governor control line). The forces are balanced across the diaphragm. So far, so good.

The mechanical lift pump is providing 15 PSI under no boost. When under boost, the mechanical pump should still be providing . . . 15 PSI at the gauge between the mechanical lift pump and the IP. Sure, the IP itself will only be getting 5 PSI's worth of differential pressure, but the gauge should still read 15 PSI regardless of the boost.

IOW, the gauge reading should not be affected by the boost pressure. You have a fuel delivery problem.

If your boost gets over around 13 PSI, you're going to have to re-think your lift pump setup. However, the Inline IPs seem to be very tolerant of low feed pressure in my experience.

waynosworld wrote:

. . . I added an electric fuel pump back by the tank and wired it into the key and finally got fuel, I buttoned everything up and took it for a drive, I got 10 miles and right after I hit the second up grade it started losing power again . . .

You've replaced the lift pump once. To eliminate something like a weird lift pump cam problem, you might switch back to this electric pump, just for testing, and re-check the fuel pressure gauge.

The needle on the gauge was moving wildly at an idle and up to 2000rpms, and I am talking about I could hear it in it's housing slamming around, I thought for sure it would break and it did on the test drive, I made it to when I lost power and seen the needle getting down lower than 4psi, but then when I let off the pedal, the rpms dropped and it went wild again and the next time I looked at it the needle was going around in circles.

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I put the gauge in the line going from the main fuel filter to the front of the inline injection pump(feed line), when I was driving it looked to have 15/20psi fuel pressure and then it started dropping and I started losing power, but when I let off the pedal and the rpms dropped the needle would just go wild.I am not sure how the lift pump could be effected by the boost, the injection pump pressurizes the fuel to a very high PSI and atomizes the fuel as far as I know, I thought it was hundreds of PSI if not thousands, I have had it up to 20psi boost, but all my issues are at 5 to 10psi boost, and I have both trucks(521/720) set to dump at around 12psi, the 720 has no issues so far, and the 521 had no issues till that trip back from Hood River after it got warm outside, the 521(this truck) loses power at 5/6psi at hiway speeds(2500rpms).

I will have to likely buy another gauge to test lines again as you can see the one I bought is likely toast, it was a $30.00 gauge(lasted 10 minutes max) and I really don't want to ruin an expensive one, I believe it is a fuel delivery issue or some how air is getting into the injection pump.So you are saying that the lift pump provides 15psi to the fuel filter/injection pump, so anything over 15psi gets ejected out the fuel filter thru the return line via that spring loaded banjo bolt?I also replaced that banjo bolt with new one I had, it was the second or third thing I did.I have pulled that return line off the fuel filter housing nipple before(the one with 2 fittings) while the engine was running and nothing came out, I even revved it, the return line in my temporary tank was also dry when I finished the test drive yesterday.

_________________I know the voices are not real, but they have some really good ideas.

If you want to eliminate variables, prop the wastegate rod open and drive it while watching the gauge. My money is on you still having loss of power. I just do not think the turbo has anything to do with this.

But you need to get another gauge on there. If you see that wild pressure fluctuation again, stop and remove the gauge (or pinch off the line) to avoid killing another gauge.

You might make your next test point for the gauge tee at the vacuum side of the lift pump. You already know there's a problem on the pressure side. May as well make certain you don't have excessive vacuum (which, in my experience, is exactly the most common problem).

OK, I am not saying it is fixed yet, but I just took it on a 20 mile drive again after changing one thing from the way it was yesterday, the pre-filter.Now a little history of Wayno, in 2008(maybe 2007) I bought a 1982 Datsun 720 diesel truck, I put 25,000 miles on it in 2/3 years of driving, it had the exact same pre-filter I have been using on this truck since them 2 cheap(99 cents) pre-filters plugged up, one within 3 tanks(Hood River trip), I then switched to these more expensive filters that my 1982 Datsun 720 diesel had that I mentioned above.I am having a hard time believing that this was the issue, there is/was no restriction when I blew into the one half hour old one I used on the trip to Canby, I used this filter for a few years on my 1982 diesel.I went to the auto parts store yesterday and bought that gauge which I had to find myself on the wall behind the counter as the guy looked right at it and passed right by, I also bought some fuel line, I also asked for a diesel pre-filter, the guy took a very long time trying to find one, I finally said there has to be one for the diesel Mercedes or a diesel BMW, that finally got me a diesel pre-filter, that is what I used on this drive and I had no power loss.Now I need to start putting it back to the stock tank and lines and hope the power loss doesn't start happening again.I did find out one thing other than what pre-filter needs to be used on this truck, I found out there is more power to be had if one puts a valve in the IP vent line, this controlled leak helps the injection pump move to a slightly richer position, it still has lots of power without that controlled leak, but there is more to be had there that I would have never known about without going thru all this I just went thru, and it is a noticeable difference, as I pulled the valve off the end of the line and pinched it off and could feel a little less power, but when I quit pinching it off I would go, I could let off the pedal a little.The truck ran way hotter than I was liking this test drive, I will look into a 3 core radiator in the coming weeks if this power loss issue is fixed.I also will look into one of them nice pre-filters with a water trap and a hand primer, I have no idea where I will find room to install it, but I believe this will be the best way to go.

I still have a problem with this pre-filter I was using being the issue, the 720 turbodiesel has them really cheap ones on it and has no issues, but I have not taken that truck on any long trips either since it was turbocharged, just around town driving, but I put 10s of thousands of miles on it non-turbo and never had an issue like this with them really cheap filters, I have been using both types for 10 years.

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And this expensive type appears to be the one that has caused me my issues, but as I said, I don't know for sure yet, as I babied the truck on the last test drive as the water temp was really high, too high for me.

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_________________I know the voices are not real, but they have some really good ideas.

Wish I had read that about the pre-filters sooner, and I am certainly happy I coaxed Al into commenting on this thread.The pre-filter I had in my 1982 Datsun 720 diesel certainly must have been the proper one even though the gas filter looks exactly the same, there is a dimple on the firewall where the mount hole is supposed to be for the pre-filter holder clip on the earlier models that didn't come with the pre-filter.I went straight from the cheapo gas filters to this gas pre-filter that looked like the one in my 1982, the cheapo gas pre-filters lasted a year or two(depended on how much driven) before they would get sucked flat and the engine would start missing from fuel starvation, I always had one in the glove compartment and it was fairly easy to change.Since I changed the 720 over to a turbodiesel, I changed that trucks pre-filter over to that type with a water trap(it came with the engine), at that time I removed the cheapo filter back by the tank.I will likely put the fuel system back to how it was before all this started today, I will also take the pre-filter part numbers and see if I can get a pre-filter that fits in the clip I mounted to the inner fender well and use that instead of what I did yesterday as the fuel lines are to the point of almost kinking using this diesel pre-filter I bought which would also cause me issues.

Also there is a screen in the bottom lift pump banjo bolt, does anyone have a part number for that screen, I broke my new one putting it back in the banjo bolt to aggressively I guess, I used the old one out of the other lift pump I removed, it was really dirty.

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_________________I know the voices are not real, but they have some really good ideas.

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